Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $200.45   11.629%   $223.7603   $223.76   $223.75   $223.80  
  Purchase #2 $220.30   4.301%   $229.7751   $229.78   $229.80   $229.80  
  Purchase #3 $195.39   5.419%   $205.9782   $205.98   $206.00   $206.00  
  Purchase #4 $59.88   6.705%   $63.895   $63.90   $63.90   $63.90  
  Purchase #5 $220.63   7.175%   $236.4602   $236.46   $236.45   $236.50  
  Purchase #6 $234.58   10.764%   $259.8302   $259.83   $259.85   $259.80  
  Purchase #7 $249.96   11.829%   $279.5278   $279.53   $279.55   $279.50  
  7 purchase totals = $1,381.19       $1,499.2268   $1,499.24   $1,499.30   $1,499.30